XBMC is best run as a stand alone machine.
I would go for either the live install version, as this has everything you need, so you don't need to have an operating system for the machine. The live install, will install a basic version of Linux so XBMC will run.
My version runs Ubuntu 10.04LTS (long term support) and then I installed the linux version of XBMC, you can do this via Ubuntu and its software manager.
I have all my media on a home built networked attached storage device (NAS).
I used server elements NAS lite.
You could get the HV to control the XBMC via IR commands. And or use one of these.
If you went the full ubuntu install you could run the HVXL software in Linux, so it would be possible to control your HV via XBmC (well in theory anyway).